Method of aluminizing a cathode-ray tube screen

ABSTRACT

A cathode-ray tube image screen panel having phosphor materials thereon is covered by a thin aluminum layer to provide a mirror effect for reflecting the light emitted by the phosphor forward to increase the brightness of the cathode-ray tube. The inventive method prevents blistering of the aluminum layer during bakeout. An organic decomposable base layer is first applied over the phosphor material. A solution comprising a volatilizable crystalline solute dissolved in a suitable solvent is provided and is coated over the base layer and allowed to dry so that the solute crystalizes. Thereafter an aluminum layer is formed over the crystalized solute which pierces the aluminum to allow escape of gases generated when the organic base layer decomposes and the crystalline solute vaporizes during bakeout.

United States Patent 1191 Lerner et al.

[5 METHOD or ALUMINIZING A CATHODE-RAY TUBE SCREEN Inventors: Martin L. Lerner, River Forest; Roy

Maskell, Oak Park, both of 111.

Zenith Radio Corporation, Chicago, Ill.

Assignee:

Filed:

Appl. No.:

Apr. 28, 1972 u.s. c1 ..117 33.s CM, 117/335 CP.

117/35 v, 117/46 CA, 117/71 R Int. Cl C03c 17/12, I-lOlj 31/20 Field 01 Search 117/335 CM, 33.5 CP, 35 v; 1 313/89 5 6] References Cited UNITED STATES PATENTS 4/1971 Schniepp 117/335 CM 6/1971 Saulnier 117/35 V 6/1971 Saulnier 117/35 V 1451 June 28,1974

Primary Examiner-William D. Martin Assistant Examiner-William R. Trenor V Attorney, Agent, or Firm-Terry M. Blackwood; Nicholas A. Camasto 5 7 ABSTRACT A cathode-ray tube image screen panel having phosphor materials thereon is covered by a thin aluminum layer to provide a mirror effect for reflecting the light emitted by the phosphor forward to increase the brightness of the cathode-ray tube. The inventive method prevents blistering of the aluminum layer during bakeout. An organic decomposable base layer is first applied over the phosphor material. A solution comprising a volatilizable crystalline solute dissolved in a suitable solvent is provided and is coated over the base layer and allowed to dry so that the solute crystalizes. Thereafter an aluminum layer isformed over the crystalized solute which pierces the aluminum to allow escape of gases generated when the organic base layer decomposes and the crystalline solute vaporizes during bakeout.

13 Claims, 2 Drawing Figures METHOD OF ALUMINIZING A CATHODE-RAY TUBE SCREEN BACKGROUND OF THE INVENTION The present invention concerns a method of applying an aluminum layer to the phosphor screen of a cathode-ray tube. This has become known in the art as aluminizing the screen. Its primary purpose is to impart to the back surface of the screen the property of specular reflection to the end that maximum brightness may be attained by directing all of the light generated in the screen to the faceplate of the tube. The aluminum layer is porous to the high velocity electrons from the electron guns, but provides a conductive return path when they have impacted the phosphor screen.

While the desirability of aluminizing is thoroughly known, the techniques of achieving it are many and varied especially in processing the screen of a color picture tube. Although the process to be described is applicable to the fabrication of monochrome screens, it is of particular benefit in aluminizing the screens of color tubes and will be described in that environment.

The screen of. a color tube comprises an ordered array or interlacing of a number of different deposits of phosphor and in the most conventional case, featuring three colors, the deposits are in the form of dots grouped in triads arranged throughoutthe screen surface; each triad including a dot of red, a dot of blue, a

dot of green phosphor. However these phosphor deposits are applied to the screen, their surface is irregular for a variety of reasons, including variations in particle size of the phosphor material. Obviously, if a layer of aluminum were to be applied to such deposits, and this could be accomplished by the well-known technique of vaporizing an aluminum pellet, the aluminum film would have a highly irregular surface since it would tend to conform to the surface contour of the phosphor layer. lrregularities in the aluminum film destroy the desired property of specular reflection and are to be avoided. In order to avoid this difficulty the art teaches the application of a film layer of volatilizable organic material over the phosphor of the screen to form a smooth substrate or base upon which the aluminum layer may be formed. Such a base allows formation of a smooth metal layer essential for increased brightness and is easily decomposed by heat during the bakeout process.

Using prior art techniques for applyingthe aluminized layer often gives rise to problems during bakeout since the gases evolved from volatilization of the organic base layer must pass through the aluminum layer. Although the aluminum layer is relatively thin, commonly about 12 microns thick, it does provide a barrier to the gases evolved. For any number of reasons, the metal layer may not'allow the gases to escape rapidly enough to prevent damage to the aluminum layer,

phosphor screen or both. If, for example, an excessively heavy film base is applied to thescreen, the amount of gases evolved may locally lift up the aluminum layer such that it will blister or become loose. Since the 2 particles causingarcing within the tube and dark spots upon the screen.

Generally the smoother the surface of the organic film base, the smoother the resulting aluminum layer, thus improving its'specular reflection and increasing tube brightness. A smoother film surface may be achieved by forming a thicker organic film base on the screen, butas mentioned above, this technique generally causes blistering during bakeout. Blistering is more pronounced at the edges of the image screen where organic film build up normally occurs during application. In a conventional two piece color tube envelope including a panel and a funnel, the image screen is formed in the panel on a clear spherically contoured faceplate portion which blends into an upstandingsurrounding wall. The transistional area between the faceplate and the surrounding'wall is commonly referred to as a heel radius. The present invention along with its other advantages is particularly suited for precluding blistering of the 'aluminized layer in the heel radius portions of the faceplate.

Accordingly, it is an object of the present invention to provide an improved method of applying a reflective aluminum layer to the screen of a cathode-ray tube.

It is a specific object of the invention to provide such a method which minimizes blistering of the aluminum layer during heat processing.

It is a furtherobject of the present invention to provide a method of applying a reflecting aluminum layer to the screen of a cathode-ray tube which produces an aluminum reflecting layerwith specular reflecting properties heretofore unobtainable.

It is a still further object of the present invention to provide a method of applying a reflecting aluminum layer to the screen of a cathode-ray tube which avoids blistering at the heel radius of the screen.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description in conjunction with the accompanying drawings, and in the several figures of which like reference numerals indicate identical elemets and in which:

FIG. 1 is a fragmentary cross-sectional view of an image screen panel at a particular stage of the inventive method embodying the present invention; and

FIG. 2 is a fragmentary cross-sectional view of an image screen panel after being processed by a method embodying the present invention.

DESCRIPTION or THE PREFERRED EMBODIMENT Referring now to FIG. 1, faceplate panel 10 is of a clear glass and has deposited thereon phosphor materials 11 and 12. The particular faceplate illustrated in FIG. 1 is of the type which features what has become to be known as black surround in that the phosphor materials are separated by light absorbing material 13 which, as well known in the art, improves the brightness and contrast of the finished tube. Although the invention will be described in this context, it is of course to be understood that the invention applies equally well to conventional color and monochrome cathode-ray tubes.

To provide a smooth surface for the aluminum layer, a decomposable smoothing material or film base 14 is applied over the image screen and the heel radius (not illustrated) of the panel. The film base may be of any type conventional for this purpose and may be applied by any of the well known filming processes such as emulsion or spray filming. In spray filming for example it is common to first wet the image screen phosphor areas with water while rotating the image screen panel and apply the film base over the wetted areas. Commonly used substances are organic decomposable materials such as acrylic or nitrocellulose base lacquers. After the film base application, it is thoroughly dried.

After the film base is completely dry, a solution comprising a vaporizable solute dissolved in a suitable solvent, which precipitates minute particles of the solute upon drying is applied over the film base by spraying or any other suitable technique. In its preferred form the solute may be a crystalline volatilizable material which forms a crystalline needlepoint structure upon drying. As shown in FIG. 1, the solution is applied and allowed to dry forming crystalline needlepoints 15 shown pro: jecting upward. The illustrations'of course are grossly exaggerated and simplified. The solution of crystalline solute is also applied over the heel radius areas and all other areas of the cathode-ray tube which are to be aluminized and have the decomposable organic film base applied thereto.

The aluminum layer is then formed over the image screen panel and other areas to be aluminized by any of the well known techniques. During formation, aluminum layer 16 is punctured by the minute particles of crystalline needlepoints 15. After the aluminum layer is formed, the image screen panel is ready'for baking to decompose film base 14 and the organic binder in the phosphor deposits, and vaporize the volatilizable crystals 15. This is done by placing the image screen panel in an environment elevated to a temperature of approximately 400 C. The film'base, crystals, and organic binder in the phosphor decompose or vaporize and evolve gases which escape through the minute holes formed in the aluminum layer by crystalline needlepoint particles 15. The large number of the tiny holes in the layer allow application of a thicker film base to the image screen panel which improves the reflectivity of the aluminum. With normal methods of application, the aluminum layer would be subject to blistering since it would not be porous enough to freely vent the evolved gases. However, with the invention the aluminum layer has minute holes formed by the crystalline needlepoints, and freely vents all of the gases evolved from the decomposable or vaporizable materials.

A preferred crystallizing solution for use with the inventive method is an aqueous solution of ammonium oxalate. An ammonium oxalate water solution forms needlepoint crystalline structures upon drying. The solution may be prepared by making up a saturated solution of ammonium oxalate in de-ionized water and then filtering the solution to separate the undissolved crystals from the solution. Thereafter to percent of extra deionized water is added to make the solution sub-saturated. A sub-saturated solution is preferred to preclude formation of crystals within the supply tank or the supply equipment used to apply the solution to the screen. Two or three drops per gallon of solution of a 4 surfactant, such as Triton CF54 manufactured by Rohme and Haas Co. may be added to facilitate spreading of the solution over those areas to which itis applied.

Solutes other than ammonium oxalate may also be employed in practicing the invention and these include; ammonium benzoate, ammonium acetate, ammonium nitrate, and citric acid. These solutes all have the property of forming minute particles of the crystalline variety. It is desirable that the solute has a limited solubility in water and preferably should not be any more soluble than 150 grams of solute per grams of water at 20 C. All of the aforementioned substances have this quality. The limited solubility assures that, upon drying, the minute particles precipitated will be spread over all those areas to which the solution is applied and not confined to localareas. A high solubility solute tends to precipitate in the last to dry areas and would not yield desirable results.

The alternative solutes mentioned are also capable of withstanding decreased atmospheric pressures down to 10-4 torr without vaporizing, one torr being equal to one millimeter of mercury in pressure. These criteria are necessary since the aluminizing is performed under vacuum to decrease the vapor pressure of the aluminized material and to assure that the molecules of. aluminum do not disperse into an atmospheric medium so that they engage the image screen uniformly. As earlier mentioned, the solutes are all vaporizable by heat at temperatures occuring during bakeout. Solute vaporization assures that essentially no solute residue remains.

An image screen panel, after being processed in accordance with the present invention, is illustrated in FIG. 2. Face-plate glass 10 has deposited thereon phosphor materials 11 and 12 separated by light absorbing material 13 as previously described in FIG. 1. Aluminum layer 16 is now draped across the various phosphor materials as shown and is relatively smooth thus providing a mirror for reflecting light emitted by the phosphor materials. Aluminum layer 16 has a myriad of pinholes 17 which allowed evolved gases to escape during bakeout. These minute holes precluded the aluminum from lifting and blistering during bakeout. However, the holes in layer 16 are so small that their total 'area is about 9% of 1 percent of the entire screen area and do not affect the reflectivity of layer 16. By practicing the inventive method more smoothing material may be used thus facilitating a smoother aluminum layer having'improved specular reflective qualities resulting in an image screen capable of displaying a brighter picture. Blistering of the aluminum layer is avoided, even in those areas such as the heel radius where excessive buildup of smoothing material is common. This precludes aluminum particles from floating within the finished cathode-ray tube, preventing serious consequences such as arcing of the electron gun or guns of the cathode-ray tube. Further, more smoothing material than heretofore possible may be used to obtain a cathode-ray tube having increased brightness.

While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

We claim: 1. In the manufacture of a cathode-ray tube having a frontal portion comprising a substantially clear faceplate blending into an upstanding surrounding wall at a heel radius, said faceplate having phosphor materials deposited thereon, a method of applying an aluminum layer over said faceplate and said heel radius which avoids blistering of said aluminum layer at least in the heel radius portions during bakeout, comprising the steps of:

applying a decomposable smoothing material over at least said phosphor material and said heel radius, such decomposable smoothing material being decomposable by heat during bakeout; providing a solution comprising a crystalline solute dissolved in a suitable solvent; said crystalline solute having the following properties: a. being vaporizable by heat at temperatures up to and including the highest temperature reached during bakeout and so as to leave essentially no residue,

b. a vapor pressure sufficient to preclude vaporization of said solute during formation of said aluminum layer, and

0. physical and chemical compatibility with said aluminum layer; t

applying said solution on the decomposablesmoothing material on said heel radius;

.drying said solution coating to allow said solute to crystalize;

forming said aluminum layer over the crystalized solute and at least said faceplate and said heel radius,

said crystalized solute puncturing, prior to bakeout, said aluminum layer in said heel radius; and

thereafter baking said tube frontal portion so as to decompose said decomposable material and vaporize said solute, the evolved gases escaping through holes formed prior to said baking in said aluminum layer by said solute.

2. A method in accordance with claim 1 which comprises the additional step of drying said decomposable smoothing material prior to the coating of said heel radius with said solution.

3. A method in accordance with claim 1 where said solution is sub-saturated.

4. A method in accordance with claim 1 where said crystalline solute has a limited solubility in said suitable solvent to assure that said solution crystalizes uniformly over said heel radius.

5. A method in accordance with claim 1 where said crystalline solute is ammonium oxalate.

6. In the manufacture of a cathode-ray tube, a method of providing an image screen panel with phosphor materials covered by an aluminum layer to provide a mirror for reflecting the light emitted by said phosphor forward to increase the brightness of said cathode-ray tube which method prevents blistering of said aluminum layer and comprises the steps of:

depositing onto said image screen said phosphor materials;

applying a decomposable material over said image screen, said material being decomposable by heat duringbakeout; V

providing a solution comprising a solute dissolved in a suitable solvent, said solution precipitating minute particles ofsaid solute upon drying, and said solute having the following properties:

a. being vaporizable by heat at temperatures up to and including the highest temperature reached during bakeout and so as to leave essentially no residue,

b. a vapor pressure sufficient to preclude vaporization of said solute during formation of said aluminum layer, and

0. physical and chemical compatibility with said aluminim layer;

applying said solution on the decomposable smoothing material on said'image screen panel;

drying said solution coating to allow said minute solute particles to form;

forming said aluminum layer over the solute particles on said image screen allowing said aluminum layer to be punctured, prior tobakeout, by said minute solute particles; and thereafter baking said screen panel so as to decompose said decomposable material and vaporize said solute, the evolved gases escaping through holes formed prior to said baking in said aluminim layerby said solute.

7. A method in accordance with claim 1 where said crystalline solute is selected from the group consisting of:

ammonium oxalate, ammonium benzoate, ammonium acetate,'ammonium nitrate, and citric acid.

8. A method in accordance with claim 6 where said solute is selected from the group consisting of ammonium oxalate, ammonium benzoate, ammonium acetate, ammonium nitrate, and citric acid.

9. A method in accordance with claim 6 where said solute is a crystalline solute, and where said solution crystalizes upon drying.

10. A method in accordance with claim 6 which com prises the additional step of drying said decomposable material prior to the coating of said image screen panel with said solution.

11. A method in accordance with claim 6 where said solution is sub-saturated.

12. A method in accordance with claim 6 where said solute has a limited solubility in said suitable solvent to assure that said solution precipitates said minute particles unifomily over said image screen panel.

13. A method in accordance with claim 6 where said crystalline solute is ammonium oxalate. 

2. A method in accordance with claim 1 which comprises the additional step of drying said decomposable smoothing material prior to the coating of said heel radius with said solution.
 3. A method in accordance with claim 1 where said solution is sub-saturated.
 4. A method in accordance with claim 1 where said crystalline solute has a limited solubility in said suitable solvent to assure that said solution crystalizes uniformly over said heel radius.
 5. A method in accordance with claim 1 where said crystalline solute is ammonium oxalate.
 6. In the manufacture of a cathode-ray tube, a method of providing an image screen panel with phosphor materials covered by an aluminum layer to provide a mirror for reflecting the light emitted by said phosphor forward to increase the brightness of said cathode-ray tube which method prevents blistering of said aluminum layer and comprises the steps of: depositing onto said image screen said phosphor materials; applying a decomposable material over said image screen, said material being decomposable by heat during bakeout; providing a solution comprising a solute dissolved in a suitable solvent, said solution precipitating minute particles of said solute upon drying, and said solute having the following properties: a. being vaporizable by heat at temperatures up to and including the highest temperature reached during bakeout and so as to leave essentially no residue, b. a vapor pressure sufficient to preclude vaporization of said solute during formation of said aluminum layer, and c. physical and chemical compatibility with said aluminim layer; applying said solution on the decomposable smoothing material on said image screen panel; drying said solution coating to allow said minute solute particles to form; forming said aluminum layer over the solute particles on said image screen allowing said aluminum layer to be punctured, prior to bakeout, by said minute solute particles; and thereafter baking said screen panel so as to decompose said decomposable material and vaporize said solute, the evolved gases escaping through holes formed prior to said baking in said aluminim layer by said solute.
 7. A method in accordance with claim 1 where said crystalline solute is selected from the group consisting of: ammonium oxalate, ammonium benzoate, ammonium acetate, ammonium nitrate, and citric acid.
 8. A method in accordance with claim 6 where said solute is selected from the group consisting of ammonium oxalate, ammonium benzoate, ammonium acetate, ammonium nitrate, and citric acid.
 9. A method in accordance with claim 6 where said solute is a crystalline solute, and where said solution crystalizes upon drying.
 10. A method in accordance with claim 6 which comprises the additional step of drying said decomposable material prior to the coating of said image screen panel with said solution.
 11. A method in accordance with claim 6 where said solution is sub-saturated.
 12. A method in accordance with claim 6 where said solute has a limited solubility in said suitable solvent to assure that said solution precipitates said minute particles uniformly over said image screen panel.
 13. A method in accordance with claim 6 where said crystalline solute is ammonium oxalate. 